Deep virtual stereo odometry

ABSTRACT

A monocular visual odometry system includes a stacked architecture. The stacked architecture receives camera data from a monocular camera and generates a depth map. Additionally, the system includes a deep virtual stereo odometry module that receives the camera data from the monocular camera and the depth map from the stacked architecture. The calculation module initializes a keyframe of the camera data using the depth map and determines a photometric error based on a set of observation points extracted from the keyframe and a set of reference points extracted from the camera data. The calculation module determines a virtual stereo photometric term using the depth map. The calculation module also optimizes a total energy function that includes the photometric error and the virtual stereo photometric term. Using the total energy function, the calculation module generates a positional parameter of the system and provides the positional parameter to an autonomous system.

RELATED APPLICATIONS

The present application claims priority to U.S. Provisional ApplicationNo. 62/685,973 for “Deep Virtual Stereo Odometry” filed Jun. 16, 2018,which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

This disclosure relates generally to the field of robotics, and morespecifically relates to monocular visual odometry used to accuratelydetermine position and orientation of an object on which a camera of amonocular visual odometry system is rigidly mounted.

BACKGROUND

Visual odometry systems are used by a wide variety of autonomoussystems, including robotic devices, self-driving cars, securitymonitoring systems, augmented reality/virtual reality (AR/VR) systems,and other autonomous systems. In some cases, the autonomous system maydrive or fly in an environment, pick up objects, or perform otherinteractions based on information from the visual odometry system. Avisual odometry system may provide an important interface between anautonomous system and the surrounding world, enabling the autonomoussystem to interpret and react to objects around it. In some cases, areliable and accurate visual odometry system may improve operation of anautonomous system, such as by improving navigational accuracy orreducing collisions.

Based on information provided by a visual odometry system, an autonomoussystem may perform environment interactions based on an estimatedlocation of the autonomous system in the environment. In some cases, avisual odometry system provides the estimated location based on a scaleof the environment, such as a scale indicating if a particular object issmall and nearby, or large and farther away. A visual odometry systemthat is configured to provide high-accuracy estimations of scale orlocation may allow the autonomous system to avoid performing actionsthat could harm humans or cause property damage. However, visualodometry systems may rely on high cost active depth cameras or stereocamera systems to provide acceptable scale and location estimations atthe visual odometry system. Such visual odometry systems may alsorequire sensitive calibration tuning, which is also expensive and timeconsuming. Further, monocular visual odometry systems relying on asingle camera using geometric approaches inherently suffer from cameratrajectories and maps that can only be estimated up to an unknown scale.This leads to scale drift and inaccuracies in the visual odometrysystem.

SUMMARY

According to certain implementations, a monocular visual odometry systemmay perform a visual odometry process by leveraging a deep monoculardepth prediction into direct sparse odometry (DSO) as direct virtualstereo measurements. For example, a monocular visual odometry systemincludes a stacked architecture module that receives camera frame datafrom a monocular camera sensor and generates a depth map of the cameraframe data. The monocular visual odometry system also includes a deepvirtual stereo odometry calculation module. The deep virtual stereoodometry calculation module receives the camera frame data from themonocular camera sensor and the depth map from the stacked architecturemodule and initializes a keyframe of the camera frame data using thedepth map of the camera frame data. Further, the deep virtual stereoodometry calculation module determines a photometric error based on aset of observation points extracted from the keyframe and a set ofreference points extracted from a set of reference camera frames of thecamera frame data. Furthermore, the deep virtual stereo odometrycalculation module determines a virtual stereo photometric term usingthe depth map of the camera frame data and optimizes a total photometricenergy function comprising the photometric error and the virtual stereophotometric term. Upon optimizing the total photometric energy function,the deep virtual stereo odometry calculation module generates apositional parameter of the monocular visual odometry system using thetotal photometric energy function and provides the positional parameterto an autonomous system.

In another example, a method includes receiving camera frame data from amonocular camera sensor and generating a depth map of the camera framedata. Further, the method includes initializing a keyframe of the cameraframe data using the depth map of the camera frame data. Furthermore,the method includes determining a photometric error based on a set ofobservation points extracted from the keyframe and a set of referencepoints extracted from a set of reference camera frames of the cameraframe data. Additionally, the method includes determining a virtualstereo photometric term using the depth map of the camera frame data andoptimizing a total photometric energy function including the photometricerror and the virtual stereo photometric term. Moreover, the methodincludes generating a positional parameter of the monocular camerasensor using the total photometric energy function and providing thepositional parameter to an autonomous system.

In another example, a non-transitory computer-readable medium embodyingprogram code for operating a monocular visual odometry system isprovided. The program code includes instructions which, when executed bya processor, cause the processor to perform operations. The operationsinclude receiving camera frame data from a monocular camera sensor andgenerating a depth map of the camera frame data. Further, the operationsinclude initializing a keyframe of the camera frame data using the depthmap of the camera frame data. Furthermore, the operations includedetermining a photometric error based on a set of observation pointsextracted from the keyframe and a set of reference points extracted froma set of reference camera frames of the camera frame data. Additionally,the operations include determining a virtual stereo photometric termusing the depth map of the camera frame data and optimizing a totalphotometric energy function including the photometric error and thevirtual stereo photometric term. Moreover, the operations includegenerating a positional parameter of the monocular camera sensor usingthe total photometric energy function and providing the positionalparameter to an autonomous system.

These illustrative implementations are mentioned not to limit or definethe disclosure, but to provide examples to aid understanding thereof.Additional implementations are discussed in the Detailed Description,and further description is provided there.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, implementations, and advantages of the present disclosure arebetter understood when the following Detailed Description is read withreference to the accompanying drawings, where:

FIG. 1 is a diagram depicting an example of a monocular visual odometrysystem, according to certain implementations;

FIG. 2 is a diagram depicting an example of a stacked architecturemodule including an encoder-decoder architecture and a residualencoder-decoder architecture, according to certain implementations;

FIG. 3 is a diagram depicting an example of a deep virtual stereoodometry calculation module with a joint optimization module, accordingto certain implementations;

FIG. 4 is a diagram depicting an example of a monocular visual odometrysystem that includes a deep virtual stereo odometry calculation moduleand a camera sensor, according to certain implementations;

FIG. 5 is a flow chart depicting an example of a process for determiningpositional parameters, according to certain implementations;

FIG. 6 is an example of left-right disparity predictions used in thedeep virtual stereo odometry calculation module to generate an estimatedtrajectory, according to certain implementations; and

FIG. 7 is a block diagram depicting an example of a computing system forimplementing a monocular visual odometry system, according to certainimplementations.

DETAILED DESCRIPTION

Certain implementations described herein provide for a monocular visualodometry system that accurately performs depth predictions for anenvironment surrounding the monocular visual odometry system from asingle image source. The monocular visual odometry system may performrapid depth estimations based on a deep network that refines predicteddepth from a single image in a two-stage process. In some instances, thedeep network is trained in a semi-supervised way using photoconsistencyin stereo images and using consistency with accurate sparse depthreconstructions from stereo direct sparse odometry (stereo DSO). Thedepth estimations generated from the deep network may achieve accurateresults without scale drifting using only the single camera of themonocular visual odometry system.

In an example, depth of objects may be estimated from a single imagegenerated by the single camera of the monocular visual odometry systemwhen known information about typical sizes or appearances of objects isused by the monocular visual odometry system. A deep learning basedapproach provides the depth estimates by training deep neural networkson large amounts of data. A deep virtual stereo odometry techniquedescribed herein is able to incorporate the deep depth predictions witha monocular odometry pipeline to generate accurate depth estimations.Further, deep virtual stereo disparity for virtual direct imagealignment constraints may be used within a framework for windowed directbundle adjustment (e.g., direct sparse odometry).

Additionally, a stacked residual network architecture may be implementedthat refines disparity estimates in two stages and is trained in asemi-supervised manner. For example, stereo direct sparse odometry(stereo DSO) is used by the monocular visual odometry system to obtain asparse depth ground-truth for the semi-supervised training. Usingsemi-supervised deep learning with the stacked residual networkarchitecture, the monocular visual odometry system is able to provideaccurate sparse three-dimensional reconstructions on a set of data(e.g., an estimated depth map).

The estimated depth map may be used in a visual odometry system toprovide a position and orientation information of the individual camera.This information may be provided to an automated system, such as aself-driving vehicle, an aerial drone, a scientific probe, augmentedreality/virtual reality (AR/VR) systems, or any suitable automatedsystem that is able to operate without human interactions. The automatedsystem may interact with its surroundings based on the operationalparameters. Based on the higher accuracy information provided by thedepth map, the automated system may improve interactions with thesurrounding environment. An automated system that can improveinteractions with the environment may operate with improved efficiencyand reliability.

In addition, a monocular visual odometry system that is capable ofaccurately providing a scale estimation may reduce the use of computingresources (e.g., processing power, memory) associated with a stereovisual odometry system. The monocular visual odometry system thatprovides an accurate scale estimation based on reduced computingresources may provide additional benefits for automated systems, such aslighter-weight computing components for autonomous aerial vehicles(e.g., drones) or lower energy consumption for battery-operated devices(e.g., long-term scientific probes for interplanetary or underwaterexploration).

In some implementations, a monocular visual odometry system determinespose data that describes the position and orientation of the individualcamera of the monocular visual odometry system relative to thesurrounding environment. For example, a monocular visual odometry systemmay receive camera data. The camera data may include images of thesurroundings of the monocular visual odometry system. Based on thecamera data, the monocular visual odometry system may use a depthestimation from a trained deep learning network to determine pose dataof the individual camera. The pose data may indicate the position andorientation of the monocular visual odometry system based at least onvisual data, such as a pose determined based on image points (e.g.,points visible in an image) that are detected in the camera data. Insome cases, the monocular visual odometry system generates (or modifies)parameters for an autonomous system based on the pose data, such asparameters describing the autonomous system's position, orientation,distance to surrounding objects, scale of surrounding objects, or anyother parameter related to navigation or operation of the autonomoussystem.

Referring now to the drawings, FIG. 1 depicts an example of a computingsystem 100 in which a monocular visual odometry system 110 isimplemented. For instance, the computing system 100 may be included in(or configured to communicate with) an autonomous system, such as anautonomous or semi-autonomous vehicle that may navigate a surroundingenvironment. In some cases, the computing system 100 may be included inor communicate with a virtual autonomous system, such as acomputer-implemented simulation of an autonomous system. The computingsystem 100 may include, for example, one or more processors or memorydevices that perform operations that are described herein. In addition,the computing system 100 may include (or be able to communicate with)one or more input devices or output devices that exchange informationwith a user, another computing system, or the surrounding environment.Input devices may provide information to the computing system 100,including input devices such as sensors (e.g., camera, accelerometer,microphone), a keyboard, a mouse, a control device (e.g., a steeringwheel), or other suitable input devices. Output devices may beconfigured to receive information from the computing system 100,including output devices such as maneuvering devices (e.g., wheels,rotors, steering devices), alerts (e.g., lights, alarms) a displaydevice, or other suitable output devices.

The computing system 100 includes the monocular visual odometry system110 and one or more sensors, such as a camera sensor 105. The camerasensor 105 may provide visual data, such as digital images representingthe surrounding environment of the monocular visual odometry system 110.The visual data may include black-and-white, color, or greyscale images;still images or video sequences of images; photographic images, lineimages, or point-based images; or any other suitable type of visualdata. In an example, the camera sensor 105 is a monocular camera.

In some implementations, the monocular visual odometry system 110 mayreceive data from the camera sensor 105, such as camera frame data 115.For example, the camera frame data 115 may include one or more cameraframes that are recorded by the camera sensor 105. Each camera frame mayinclude an image of the surroundings of the monocular visual odometrysystem 110, such as images of buildings, people, road markings, or otherobjects in the surrounding environment. In addition, each camera framemay include (or correspond to) a time, such as a timestamp indicatingwhen the image was recorded by the camera sensor 105.

The monocular visual odometry system 110 may include a data processingmodule 120. The data processing module 120 may be configured todetermine pose data that describes a position and orientation of thevisual odometry system 110 relative to the surrounding environment. Forexample, the data processing module 120 may implement a stackedarchitecture 123 to identify an estimated depth map from the cameraframe data 115. The depth map generated by the stacked architecture 123may be used in conjunction with a deep virtual stereo odometrycalculation module 125 to generate information describing a pose of themonocular visual odometry system 110, such as a set of image points(e.g., extracted from one or more camera images) that indicate shapes,edges, or other visual features of the surrounding environment.

The estimated pose data may be calculated based on available datadescribing the monocular visual odometry system 110 or the environment,such as the camera frame data 115. In some cases, the data processingmodule 120 may determine the estimated data based on data that is notincluded in the camera frame data 115. For example, before or during aninitialization period of the monocular visual odometry system 110, theestimated pose data may be calculated based on an initialized estimationof position of the monocular visual odometry system 110. The initializedestimates may be based on an interaction of the camera frame data 115with the stacked architecture 123.

The data processing module 120 may optimize the pose data for themonocular visual odometry system 110 based on received data. Based onanalysis of the camera frame data 115, for example by the stackedarchitecture 123 and the deep virtual stereo odometry calculation module125, the data processing module 120 may determine an adjustment for theestimated pose. In some cases, the adjustment indicates a change of themonocular visual odometry system 110's estimated position or orientation(or both). The data processing module 120 may generate optimized posedata based on the determined adjustment. In some cases, the optimizedpose data may adjust pose data describing the position and orientationof the visual odometry system 110, such as by correcting the pose datato have a value that is closer to the actual position and orientation inthe environment. In some cases, the data processing module 120 optimizesthe pose data in an ongoing manner.

Based on the deep virtual stereo odometry calculation module 125, themonocular visual odometry system 110 may generate or modify one or morepositional parameters 185. The positional parameters 185 may describethe pose of the monocular visual odometry system 110, such as a positionin a coordinate system or an angle of orientation. In some cases, themonocular visual odometry system 110 is configured to provide thepositional parameters 185 to an autonomous system 180. The autonomoussystem 180 may perform one or more operations based on the positionalparameters 185, such as operations related to navigation, vehicularmotion, collision avoidance, or other suitable operations.

In some cases, optimizing pose data that is used by an autonomous systemimproves the capabilities of the autonomous system to interact with itsenvironment. For example, optimization of pose data, includingcontinuous or periodic optimization, may enable the autonomous system180 to determine correct navigational headings, adjust velocity,estimate a correct distance to an object, or perform other adjustmentsto its own operations. In some cases, adjusting operations based on theoptimized pose data may improve accuracy and reliability of theautonomous system's activities.

FIG. 2 depicts an example of a stacked architecture module 200 includingan encoder-decoder architecture 202 and a residual encoder-decoderarchitecture 204. The stacked architecture module 200 may be included ina monocular visual odometry system, such as the monocular visualodometry system 110 described above with regard to FIG. 1. In addition,the stacked architecture module 200 may receive data (e.g., as describedabove with regard to FIG. 1), such as camera frame data 215 received bythe camera sensor 105. In some cases, the camera frame data 215 mayinclude images generated by the camera sensor 105. Based on the receiveddata, the stacked architecture module 200 may generate a depth map 217of the images generated by the camera sensor 105. For example, thestacked architecture module 200 may modify the camera frame data 215 byadding a depth element to generate the depth map 217.

In one or more examples, the encoder-decoder architecture 202 and theresidual encoder-decoder architecture 204 are fully convolutional deepneural networks. The residual encoder-decoder architecture 204 includesfewer layers and receives an output from the encoder-decoderarchitecture 202 as an input. The residual encoder-decoder architecture204 may refine disparity maps predicted by the encoder-decoderarchitecture 202 by learning an additive residual signal.

The encoder-decoder architecture 202 may include a ResNet-50 basedencoder and skip-connections between corresponding encoder and decoderlayers. A decoder of the encoder-decoder architecture 202 upprojectsfeature maps to an original resolution and generates a pair of disparitymaps dis_(simple,s) ^(left) disp_(simple,s) ^(right) for each resolutions (e.g., where s∈[0,3]). In an example, the upprojection is implementedby a resize-convolution (e.g., a nearest-neighbor upsampling layer by afactor of two followed by a convolutional layer). The usage ofskip-connections may enable the decoder to recover high-resolutionresults with fine-grained details.

As illustrated, the encoder-decoder architecture 202 outputs a leftdisparity map 220 at a resolution of 0 (i.e., disp_(simple,0) ^(left)).The left disparity map 220 is fed into the residual encoder-decoderarchitecture 204 along with an original image 222 (i.e., I^(left)), aleft reconstructed image 224 (i.e., I_(recons) ^(left)) a rightreconstructed image 226 (i.e., l_(recons) ^(right)), and areconstruction error 228 (i.e., e_(l)), which represents areconstruction error between the original image 222 and the leftreconstructed image 224. The residual encoder-decoder architecture 204further refines the disparity maps predicted by the encoder-decoderarchitecture 202. For example, the residual encoder-decoder architecture204 learns residual signals (i.e., disp_(res,s)) to the disparity maps(i.e., disp_(simple,s)) predicted by the encoder-decoder architecture202 for both left and right images for all resolutions.

In an example, the right reconstructed image 226 is generated by warpingthe original image 222 using a right disparity map generated for aresolution s of 0 at the encoder-decoder architecture 202 (i.e.,disp_(simple,0) ^(right)) Further, the left reconstructed image 224 isgenerated by back-warping the right reconstructed image 226 using a leftdisparity map generated for a resolution s of 0 at the encoder-decoderarchitecture 202 (i.e., disp_(simple,0) ^(left)) The residualencoder-decoder architecture 204 outputs a pair of residual disparitymaps disp_(res,s) ^(left) and disp_(res,s) ^(right) for each resolutions (e.g., where s∈[0,3]).

The outputs of both the encoder-decoder architecture 202 and theresidual encoder-decoder architecture 204 are combined with element-wisesummation to generate the depth map 217. In an example, the depth map217 may be represented with the following equation:disp_(s)=disp_(simple,s)⊕disp_(res,s)s∈[0,3]  (Equation 1)where disp_(s) represents the depth map 217.

For each resolution s of the depth map 217, a loss

_(s) at each output scale s may be defined. For example, a total loss Lis represented by the following equation:

=Σ_(s=0) ³

_(s)  (Equation 2)The loss at each resolution may be a linear combination of five termsthat are symmetric in left and right images. For example, the loss ateach resolution may be represented by the following equation:

_(s)=α_(U)(√_(U) ^(left)+

_(U) ^(right))+α_(S)(

_(S) ^(left)+

_(S) ^(right))+α_(ir)(

_(ir) ^(left)+

_(lr) ^(right))α_(smooth)(

_(smooth) ^(left)+

_(smooth) ^(right))+α_(occ)(

_(occ) ^(left)+

_(occ) ^(right))  (Equation 3)where

_(U) is a self-supervised loss,

_(S) is a supervised loss,

_(lr) is a left-right consistency loss,

_(smooth) is a smoothness term encouraging predicted disparities to belocally smooth, and

_(occ) is an occlusion regularization term. The encoder-decoderarchitecture 202 and the residual encoder-decoder architecture 204 maybe trained using training data to minimize the total loss

. The training of the encoder-decoder architecture 202 and the residualencoder-decoder architecture 204 may be performed in a semi-supervisedmanner. For example, the encoder-decoder architecture 202 and theresidual encoder-decoder architecture 204 may be trained by combiningself-supervised and supervised training methods with relying on costlycollection of LiDAR ground-truth data. Instead, stereo direct sparseodometry is used to provide accurate sparse three-dimensionalreconstructions of information in the training data.

The self-supervised loss term measures the quality of the reconstructedimages. As mentioned above, the reconstructed image is generated bywarping the input image into a view of a rectified stereo image. Thequality of the reconstructed image is measured with a combination of anl_(i) loss and single scale structural similarity (SSIM). Theself-supervised loss may be represented by the following equation:

$\begin{matrix}{\mathcal{L}_{U}^{left} = {{\frac{1}{N}{\sum\limits_{x,y}{\alpha\frac{1 - {{SSIM}\;\left( {{I^{left}\left( {x,y} \right)},{I_{recons}^{left}\left( {x,y} \right)}} \right)}}{2}}}} + {\left( {1 - \alpha} \right){{{I^{left}\left( {x,y} \right)} - {I_{recons}^{left}\left( {x,y} \right)}}}_{1}}}} & \left( {{Equation}\mspace{14mu} 4} \right)\end{matrix}$

The supervised loss term measures the deviation of the predicteddisparity map from the disparities estimated by stereo direct sparseodometry at a sparse set of pixels. The supervised loss may berepresented by the following equation:

$\begin{matrix}{\mathcal{L}_{S}^{left} = {\frac{1}{N}{\sum_{{({x,y})} \in \;\Omega_{{DSO},\;{left}}}{\beta_{\in}\left( {{{disp}^{left}\left( {x,y} \right)} - {{disp}_{DSO}^{left}\left( {x,y} \right)}} \right)}}}} & \left( {{Equation}\mspace{14mu} 5} \right)\end{matrix}$where Ω_(DSO,left) is a set of pixels with disparities estimated bydirect sparse odometry and β_(∈)(x) is a reverse Huber (berHu) norm,which lets training of the stacked architecture module 200 focus onlarger residuals. A threshold E may be adaptively set as abatch-dependent value represented by the following equation:∈=0.2 max_((x,y)∈Ω) _(DSO,left) |disp^(left)(x,y)−disp_(DSO)^(left)(x,y)|  (Equation 6)

Given only a left image as input, the monocular visual odometry system110 predicts a disparity map of both the left image and the right image.Consistency between the left and right disparity image is provided bythe left-right disparity consistency loss term. The following equationmay represent the left-right disparity consistency loss:

$\begin{matrix}{\mathcal{L}_{lr}^{left} = {\frac{1}{N}{\sum_{({x,y})}{{{{disp}^{left}\left( {x,y} \right)} - {{disp}^{right}\left( {{x - {{disp}^{left}\left( {x,y} \right)}},y} \right)}}}}}} & \left( {{Equation}\mspace{14mu} 7} \right)\end{matrix}$

The disparity smoothness regularization term assumes that a predicteddisparity map should be locally smooth. A second-order smoothness prioris used and downweighted when an image gradient is high. The followingequation may represent the disparity smoothness regularization:

$\begin{matrix}{\mathcal{L}_{lr}^{left} = {{\frac{1}{N}{\sum_{({x,y})}{{{\nabla_{x}^{2}{{disp}^{left}\left( {x,y} \right)}}}e^{- {{\nabla_{x}^{2}{I^{left}{({x,y})}}}}}}}} + {{{\nabla_{y}^{2}{{disp}^{left}\left( {x,y} \right)}}}e^{- {{\nabla_{y}^{2}{I^{left}{({x,y})}}}}}}}} & \left( {{Equation}\mspace{14mu} 8} \right)\end{matrix}$

The disparity smoothness regularization tends to generate a shadow areawhere values gradually change from foreground to background due tostereo occlusion. To favor background depths and hard transitions atocclusions, the occlusion regularization term is imposed to penalize atotal sum of absolute disparities. A combination of smoothness andocclusion regularization prefers to directly take a smaller, close-bybackground disparity that better corresponds to an assumption that abackground area is uncovered. The occlusion regularization may berepresented by the following equation:

$\begin{matrix}{\mathcal{L}_{occ}^{left} = {\frac{1}{N}{\sum_{({x,y})}{{{disp}^{left}\left( {x,y} \right)}}}}} & \left( {{Equation}\mspace{14mu} 9} \right)\end{matrix}$

FIG. 3 depicts an example of a deep virtual stereo odometry calculationmodule 125 that includes a joint optimization module 330. The deepvirtual stereo odometry calculation module 125 may be included in amonocular visual odometry system, such as the monocular visual odometrysystem 110 described above with regard to FIG. 1. In addition, the deepvirtual stereo odometry calculation module 125 may receive data (e.g.,as described above with regard to FIG. 1), such as camera frame data 215received by the camera sensor 105. In some cases, the camera frame data215 may include one or more groups of camera frames, such as a group ofkeyframes 311 and a group of additional camera frames 313. Based on thereceived data, the joint optimization module 330 may modify pose data.For example, the joint optimization module 330 may modify coarsetracking associated with pose data based on the camera frame data 215,including the keyframes 311 and the additional frames 313.

In some implementations, a coarse tracking module 340 that is includedin the deep virtual stereo odometry calculation module 125 is able toadjust pose data based on one or more camera frames in the camera framedata 215. For example, the coarse tracking module 340 may receive aninitial pose estimate 329, such as pose data that includes a currentestimation of the monocular visual odometry system's position andlocation based on the camera frame data 215 (e.g., a set of image pointsextracted from camera images). The initial pose estimate 329 may beassigned based on a motion model of the camera sensor 105. Theassignment of the estimated pose data 331 may be performed by assumingcamera motion between a most recent time step t−1 and a current timestep t is the same as between a time step t−2 and the most recent timestep t−1. In addition, the coarse tracking module 340 may receive acurrent camera frame (e.g., having a timestamp indicating a recent timeof recording by a camera sensor), and a current keyframe from the groupof keyframes 311 (e.g., having the most recent timestamp from the groupof keyframes 311).

The current keyframe, and each new keyframe 311 provided to the jointoptimization module 330, may be initialized with the depth map 217generated by the stacked architecture module 200 and associated with thetime stamps of the keyframes. The coarse tracking module 340 may performa comparison between the current camera frame and the current keyframe,such as a comparison based on a direct image alignment technique. Insome cases, the deep virtual stereo odometry calculation module 125assigns the current camera frame a status as a keyframe, such as anadditional keyframe included in the group of keyframes 311. For example,a current camera frame that includes a high-quality image (e.g., lowblur, good illumination, clearly visible image features) may be assignedstatus as a keyframe. In an additional example, a current camera framethat is sufficiently different from a previous keyframe may be assignedstatus as a keyframe. In such an example, the new keyframe may beassigned when the camera sensor 115 turns a corner on a street.

Based on the comparison, the coarse tracking module 340 may determine anadjustment to the initial pose estimate 329 to generate the estimatedpose data 331. The adjustment may indicate a change in the position ororientation of the monocular visual odometry system, based on one ormore visual differences detected between the current camera frame andthe current keyframe, such as a difference between extracted points. Inaddition, the adjustment determined by the coarse tracking module 340may be based on a given type of data, such as the camera frame data 215.In some cases, the joint optimization module 330 may generate modifiedpose data 335 based on the estimated pose data 331 determined by thecoarse tracking module 340.

In some implementations, the joint optimization module 330 may perform ajoint optimization of energy functions of pose data and image depths ofsampled points jointly. For example, a factorization module 350 that isincluded in the joint optimization module 330 may receive the estimatedpose data 331, some or all of the camera frame data 215 (such as thekeyframes 311), and data associated with the depth map 217. Thefactorization module 350 may determine a joint optimization of energyfunctions associated with the estimated pose data 331 and the imagedepths of the depth map 217.

In some implementations, the joint optimization module 330 includes amarginalization module 360. In an example, the marginalization module360 removes old keyframes 311 from the deep virtual stereo odometrycalculation module 125 by marginalization. The removal of the oldkeyframes 311 maintains a fixed size of an active processing window forthe deep virtual stereo odometry calculation module 125. Additionally,parameter estimates (e.g., camera poses and depths in a marginalizationprior factor) outside of the active window may also incorporated intothe joint optimization module 330.

Based on the joint optimization of the estimated pose data 331, thefactorization module 350 may determine a bundle adjustment to theestimated pose data 331. The bundle adjustment may indicate a change inthe position or orientation of the monocular visual odometry system 110based on one or more differences in visual data. In some examples, thejoint optimization module 330 may generate modified pose data 335 basedon the bundle adjustment determined by the factorization module 350. Themodifications may include a joint optimization, such as a jointoptimization that optimizes the estimated pose data 331 (e.g., in agiven set of operations by the factorization module 350).

In some implementations, one or more of a joint optimization or a coarsetracking pose adjustment are performed in an ongoing manner. Forexample, the coarse tracking module 340 may determine a pose adjustmentfor each camera frame that is included in the camera frame data 215. Asimages are recorded by the camera sensor 115, the images may be added tothe camera frame data 215 as additional camera frames (e.g., included inthe additional frames 313). The coarse tracking module 340 may determinea respective pose adjustment for each added image, and generate (ormodify) the modified pose data 335 based on the respective adjustments.In addition, the estimated pose data 331 may be updated based on themodified pose data 335, such that the estimated pose data 331 is keptcurrent based on a joint optimization pose adjustment as images areadded to the camera frame data 215.

In some cases, a camera frame in the additional frames 313 is assignedstatus as a keyframe in the keyframes 311. For example, an additionalcamera frame that is determined to have high quality or that isdetermined to exceed a difference threshold of a previous keyframe(e.g., by the deep virtual stereo odometry calculation module 125) maybe moved to the group of keyframes 311 as an additional keyframe.Responsive to a determination that an additional keyframe has beenadded, the factorization module 350 may determine a joint optimizationbased on the additional keyframe. The factorization module 350 maydetermine a respective joint optimization responsive to each addedkeyframe, and generate (or modify) the modified pose data 335 based onthe respective joint optimization. In addition, the estimated pose data331 may be updated based on the modified pose data 335 such that theestimated pose data 331 is kept current based on a joint optimization asadditional keyframes are added to the camera frame data 215.

In some implementations, a monocular visual odometry system isconsidered a deep virtual stereo odometry system. The deep virtualstereo odometry system may include (or be configured to communicatewith) one or more of a deep virtual stereo odometry calculation moduleand a camera sensor. In addition, the deep virtual stereo odometrysystem may determine one or more positional parameters based on posedata determined from the camera sensor. In some cases, the deep virtualstereo odometry system may determine the pose data based on a minimizedenergy function that includes a photometric error. For example, the posedata may be determined based on the photometric error of a set ofpoints, such as changes in the position of the point between cameraframes. In some cases, the deep virtual stereo odometry system maydetermine the positional parameters based on the pose data (or changesto the pose data) that are indicated by the photometric error.

FIG. 4 depicts an example of a monocular visual odometry system 410 thatincludes a deep virtual stereo odometry calculation module 420 and acamera sensor 405. The monocular visual odometry system 410 may beconsidered a deep virtual stereo odometry system (e.g., a monocularvisual odometry system including the deep virtual stereo odometrycalculation module 420 and the camera sensor 405). In some cases, themonocular visual odometry system 410 may include one or more of a jointoptimization module, a coarse tracking module, a factorization module,or a marginalization module (such as described above with regard to FIG.3), and these modules may perform one or more techniques described withregard to FIG. 4. The monocular visual odometry system 410 may determineone or more positional parameters 485. Determining the positionalparameters 485 may include generating a photometric error 443 andcalculating a minimized energy function based on the photometric error443. In addition, the monocular visual odometry system 410 may provideone or more of the positional parameters 485 to an autonomous system,such as an autonomous system 480.

In FIG. 4, the deep virtual stereo odometry calculation module 420 mayreceive data recorded by the camera sensor 405, such as camera framedata 415. The camera frame data 415 may include a group of one or morecamera frames, such as a keyframe 411 or an additional frame 413, thatinclude respective images and corresponding timestamps. In some cases,the deep virtual stereo odometry calculation module 420 may receive thekeyframe 411 and a corresponding keyframe timestamp. Based on thecorresponding keyframe timestamp, the deep virtual stereo odometrycalculation module 420 may determine that the keyframe 411 is a currentkeyframe that is included in the camera frame data 415 (e.g., thekeyframe timestamp is closer to a current time than other timestamps ofother keyframes). For example, the keyframe 411 may be a recently addedkeyframe, such as a camera frame that has had its status change to akeyframe. In some cases, responsive to determining that the keyframe 411is the current keyframe, the deep virtual stereo odometry calculationmodule 420 may generate or modify pose data and geometry data based onthe keyframe 411.

The deep virtual stereo odometry calculation module 420 may also receivea depth map 417 of the camera frame data 415. As discussed above withrespect to FIG. 2, the depth map 417 may be generated by the stackedarchitecture 200. The depth map 417 may be represented as predicteddisparity maps between stereo images. Here, the disparity maps representthe disparity (i.e., apparent pixel differences) between thereconstructed right image 226 (i.e., I_(recons) ^(right)) and the leftreconstructed image 224 (i.e., l_(recons) ^(left)). Each of the newkeyframes 411 added to the deep virtual stereo odometry calculationmodule 420 includes the depth map 417 that is initialized based on thepredicted left disparity and the predicted right disparity generatedbased on the original image 222 (i.e., l^(left)), as identified by thestacked architecture 200. The predicted left disparity may berepresented as D^(L) and the predicted right disparity may berepresented as D^(R) at scale 0. In the deep virtual stereo odometrycalculation module 420, the left disparity map D^(L) is used as aninitialization depth value instead of randomly initializing the depth.By using D^(L) for initialization, scale drift associated with monocularodometry is largely avoided or minimized.

A disparity value of an image point with a coordinate p may be convertedto an inverse depth d_(p) using rectified camera intrinsics and a stereobaseline of the training data of the stacked architecture 200. In anexample, the inverse depth d_(p) may be represented by the followingequation:

$\begin{matrix}{d_{p} = \frac{D^{L}(p)}{f_{x}b}} & \left( {{Equation}\mspace{14mu} 10} \right)\end{matrix}$where b is a baseline between two cameras of a stereo camera setup, andf_(x) is a focal length of the camera sensor 105. More specifically,assuming each pixel is has a width x and a height y in meters, thenf_(x) is calculated by dividing a focal length in meters by the width xof the pixel in meters.

The deep virtual stereo odometry calculation module 420 may extract fromthe keyframe 411 a set of observation points, such as an observationpointset 412, that indicate image features visible in the keyframe 411.Non-limiting examples of image features may include edges, surfaces,shadows, colors, or other visual qualities of objects depicted in animage. In some cases, the observation pointset 412 is a sparse set ofpoints. For example, the observation pointset 412 may include arelatively small quantity of points compared to a quantity of pointsthat are available for extraction, such as a sparse set of approximately100-600 extracted points for the keyframe 411, from an image having tensof thousands of points available for extraction. The observationpointset 412 may be selected by introducing a left-right consistencycheck to filter out pixels which likely lie in an occluded area betweenthe left image and a reconstructed right image. For example, theleft-right consistency check may be represented by the followingequation:e _(lr) =|D ^(L)(p)−D ^(R)(p′)| with p′=p−[D ^(L)(p)0]^(T)  (Equation11)In an example, pixels with a left-right consistency check error (i.e.,e_(lr)) greater than one may not be selected, as the likelihood of thosepixels falling in the occluded area is too significant.

In addition, the deep virtual stereo odometry calculation module 420 mayreceive at least one reference camera frame from the camera frame data415, such as the reference keyframes 413. The reference keyframes 413may include one or more reference images and respective correspondingtimestamps, such as an image that has been recorded prior to thekeyframe timestamp of the keyframe 411. The deep virtual stereo odometrycalculation module 420 may extract from the reference keyframes 413 aset of reference points, such as a reference pointset 414, that indicateimage features visible in the reference keyframes 413. The referencepointset 414 may be a sparse set of points, such as described above. Inaddition, the reference pointset 414 may include a sparse set of pointsfor each keyframe included in the reference keyframes 413 (e.g.,approximately 1000-5000 points, based on a combination of approximately100-600 respective points for each respective reference keyframe in agroup of about eight reference keyframes). In some cases, pose data maybe based on one or both of the observation or reference pointsets 412 or414. For example, the estimated or modified pose data 331 or 335 maydescribe poses based on extracted points (such as points from thepointsets 412 or 414).

Each new frame provided by the camera frame data 415 may be tracked withrespect to the reference keyframes 413 using direct image alignment in acoarse-to-fine manner. After this comparison, the deep virtual stereoodometry calculation module 420 decides if a new keyframe 411 should becreated for the newly added frame. When a new keyframe 411 is added, atotal energy function (i.e., including a temporal multi-view energyfunction and a virtual stereo energy function) is optimized. Thetemporal multi-view energy function may be represented by the followingequation:E _(photo):=

Σ_(j∈obs(p)) E _(ij) ^(p)  (Equation 12)where

is a fixed-sized window containing active keyframes such as the keyframe411 and the reference keyframes 413,

_(i) is a set of points selected from a host keyframe with an index i(i.e., the observation pointset 312 and the reference pointset 314), andj∈obs(p) is an index of the keyframes (e.g., the keyframe 411 and thereference keyframes 313) that observes the point p. Further, E_(ij) ^(p)is a photometric error 443 of the point p when projected from a hostkeyframe (e.g., the keyframe 311) onto another keyframe (e.g., thereference keyframes 413). The photometric error may be represented bythe following equation:

$\begin{matrix}{E_{ij}^{p}:={\omega_{p}{{\left( {{I_{j}\left\lbrack \overset{\sim}{p} \right\rbrack} - b_{j}} \right) - {\frac{e^{a_{j}}}{e^{a_{i}}}\left( {{I_{i}\lbrack p\rbrack} - b_{i}} \right)}}}_{\gamma}}} & \left( {{Equation}\mspace{14mu} 13} \right)\end{matrix}$where the point p is included in a first image I_(i). Parameters a_(i),a_(j), b_(i), and b_(j) are used for modeling an affine brightnesstransformation, and a weight ω_(p) penalizes points with high imagegradient with an intuition that an error originating from bilinearinterpolation of discrete image values is larger. The ∥.∥_(γ) is theHuber norm with a threshold γ. A difference of an intensity of the pointp is determined between the first image I_(i) (e.g., from the keyframe311) and a second image I_(j) (e.g., from a keyframe in the referencekeyframes 413). The point {tilde over (p)} is a projected imagecoordinate using a relative rotation matrix R∈SO(3) and translationvector t∈

³. The point {tilde over (p)} may be represented by the followingequation:{tilde over (p)}=Π _(c)(RΠ _(c) ⁻¹(p,d _(p))+t)  (Equation 14)where Π_(c) and Π_(c) ⁻¹ are camera projection and back-projectionfunctions.

The deep virtual stereo odometry calculation module 420 may determinethe photometric error 443 based on the observation pointset 412 andreference pointset 414. For example, the deep virtual stereo odometrycalculation module 420 may compare an observed intensity of one or morepoints in the observation pointset 412 to a reference intensity of oneor more corresponding points in the reference pointset 414. Thephotometric error 443 may be based on a combination of the comparedintensities, as described above in Equation 12.

To further improve the accuracy of the photometric error 443, a virtualstereo photometric term E^(†p) is introduced for each point p. Thevirtual stereo photometric term may be represented by the followingequation:E _(i) ^(†p):=ω_(p) ∥I _(i) ^(†)[p ^(†)]−I _(i)[p]∥_(γ) with I _(i)^(†)[p ^(†)]=I _(i)[p ^(†)−[D ^(R)(p ^(†))0]^(T)]   (Equation 15)where p^(†)=Π_(c)(Π_(c) ⁻¹(p,d_(p))+t_(b)) is a virtual projectedcoordinate of p using a vector t_(b) denoting a virtual stereo baselinethat is obtained from training the stacked architecture 200. The virtualstereo photometric term E^(†p) may optimize an estimated depth of thevisual odometry to become consistent with the disparity prediction(e.g., the depth map 217) generated by the stacked architecture 200.Instead of imposing consistency directly on estimated and predicteddisparities, residuals are formulated in photoconsistency to reflectuncertainties of the prediction of the stacked architecture 200 and tokeep a unit of the residuals consistent with temporal direct imagealignment terms.

The energy may then be optimized using the following equation:E _(photo):=

(λE _(i) ^(†p) +Σj∈obs(p)E _(ij) ^(p))  (Equation 16)where a coupling factor λ balances the temporal term and the virtualstereo photometric term. Based on the photometric error 443, the deepvirtual stereo odometry calculation module 420 may calculate a minimizedenergy function. For example, all of the parameters of the total energymay be jointly optimized using the Gauss-Newton method.

In some implementations, pose data, such as the modified pose data 335,may be modified based on the photometric error 443. In some cases, themonocular visual odometry system 410 may generate (or modify) thepositional parameters 485 based on the minimized values of thephotometric error 443. The positional parameters 485 may be provided tothe autonomous system 480.

FIG. 5 is a flow chart depicting an example of a process 500 fordetermining positional parameters based on a photometric error. In someimplementations, such as described in regard to FIGS. 1-4, a computingdevice executing a deep virtual stereo odometry system implementsoperations described in FIG. 5, by executing suitable program code. Forillustrative purposes, the process 500 is described with reference tothe examples depicted in FIGS. 1-4. Other implementations, however, arepossible.

At block 510, the process 500 involves receiving the camera frame data215 from the camera sensor 105. The camera frame data may include thekeyframes 211, additional frames 213, or any other data obtained by thecamera sensor 105. In an example, the camera sensor 105 is an individualcamera, and the camera frame data 215 is monocular camera data.

At block 520, the process 500 involves generating the depth map 217 byprocessing the camera frame data with the stacked architecture 200. Asdiscussed above with respect to FIG. 2, the stacked architecture 200includes the encoder-decoder architecture 202 and the residualencoder-decoder architecture 204. The camera frame data 215 is processedby the encoder-decoder architecture 202 and the residual encoder-decoderarchitecture 204 to generate the depth map 217. In an example, the depthmap 217 may represent a predicted left disparity D^(L) and a predictedright disparity D^(R).

At block 530, the process 500 involves initializing keyframes using thedepth map 217. Initially, the deep virtual stereo odometry calculationmodule 125 determines which data of the camera frame data 215 representsa new keyframe 311. Upon identifying the new keyframe 311, the deepvirtual stereo odometry calculation module 125 initializes depth maps ofthe new keyframes 311 using the predicted left disparity D^(L) and thepredicted right disparity D^(R) predicted by the stacked architecturemodule 200.

At block 540, the process 500 involves determining a photometric errorbased on a set of observation points extracted from the keyframe 311 anda set of reference points extracted from reference camera frames. Insome cases, the set of observation points and the set of referencepoints may each be a sparse set of points, such as the observationpointset 412 and the reference pointset 414. In some implementations,the photometric error is based on a comparative intensity of one or moreobservation points as compared to respective reference points. Forexample, the deep virtual stereo odometry calculation module 420 maydetermine the photometric error 443 based on a comparison of eachobservation point in the observation pointset 412 to a respectivecorresponding reference point in the reference pointset 414.

At block 550, the process 500 involves optimizing a total photometricenergy function using the photometric error. In an example, the totalphotometric energy function may include the photometric error 443 and avirtual stereo photometric term, as discussed above with respect to FIG.4. The total photometric energy may be jointly optimized using the GaussNewton method. Other energy optimization techniques are alsocontemplated.

At block 560, the process 500 involves generating positional parametersof the monocular visual odometry system 110 based on the optimizedphotometric energy. For example, the monocular visual odometry system410 may generate the positional parameters 485 based on the photometricerror 443 after the photometric energy function is optimized. In somecases, the positional parameters are provided to an autonomous system,such as to the autonomous system 480, and are used to control operationof the autonomous system 480 (e.g., steering, navigating, etc.).

In some implementations, one or more operations in the process 500 arerepeated. For example, some or all of the process 500 may be repeatedbased on additional camera frame data being received (or generated) bythe monocular visual odometry system. In some cases, the deep virtualstereo odometry calculation module may perform additional comparisons ofmodified observation and reference pointsets, such as ongoingcalculations of the photometric errors based on additional camera framedata.

FIG. 6 is an example of left-right disparity predictions used in thedeep virtual stereo odometry calculation module 125 to generate anestimated trajectory. The camera frame data 215 provided to the stackedarchitecture module 200 to generate the depth map 217 is depicted inFIG. 6 as a monocular camera image. The depth map 217 generated by thestacked architecture module 200 includes a predicted left disparity map602 and a predicted right disparity map 604.

By initializing the new keyframes 311 in the deep virtual stereoodometry calculation module 125 with the predicted left disparity map602 and the predicted right disparity map 604, scale drift is avoided asthe monocular visual odometry system 110 moves, for example, along acity street. Thus, the monocular visual odometry system 110 canaccurately plot a location of the monocular visual odometry system 110based on the monocular images received from the camera sensor 105. Thelocation plotting is demonstrated by an estimated trajectory 606 of themonocular visual odometry system 110 that is generated as the monocularvisual odometry system 110 moves. As depicted by image 608, theestimated trajectory 606 may be representative of the path of themonocular visual odometry system 110 through a street 610 within a city.In an example, the autonomous system 480, described above with respectto FIG. 4, may use the estimated trajectory 606 to control operation ofa self-driving car.

Any suitable computing system or group of computing systems can be usedfor performing the operations described herein. For example, FIG. 7 is ablock diagram depicting a computing system 701 that is configured as amonocular visual odometry system, according to certain implementations.

The depicted example of a computing system 701 includes one or moreprocessors 702 communicatively coupled to one or more memory devices704. The processor 702 executes computer-executable program code oraccesses information stored in the memory device 704. Examples ofprocessor 702 include a microprocessor, an application-specificintegrated circuit (“ASIC”), a field-programmable gate array (“FPGA”),or other suitable processing device. The processor 702 can include anynumber of processing devices, including one.

The memory device 704 includes any suitable non-transitorycomputer-readable medium for storing the deep virtual stereo odometrycalculation module 125, the stacked architecture module 200, and otherreceived or determined values or data objects. The computer-readablemedium can include any electronic, optical, magnetic, or other storagedevice capable of providing a processor with computer-readableinstructions or other program code. Non-limiting examples of acomputer-readable medium include a magnetic disk, a memory chip, a ROM,a RAM, an ASIC, optical storage, magnetic tape or other magneticstorage, or any other medium from which a processing device can readinstructions. The instructions may include processor-specificinstructions generated by a compiler or an interpreter from code writtenin any suitable computer-programming language, including, for example,C, C++, C #, Visual Basic, Java, Python, Perl, JavaScript, andActionScript.

The computing system 701 may also include a number of external orinternal devices such as input or output devices. For example, thecomputing system 701 is shown with an input/output (“I/O”) interface 708that can receive input from input devices or provide output to outputdevices. A bus 706 can also be included in the computing system 701. Thebus 706 can communicatively couple one or more components of thecomputing system 701.

The computing system 701 executes program code that configures theprocessor 702 to perform one or more of the operations described abovewith respect to FIGS. 1-6. The program code includes operations relatedto, for example, one or more of the deep virtual stereo odometrycalculation module 125, the stacked architecture module 200, or othersuitable applications or memory structures that perform one or moreoperations described herein. The program code may be resident in thememory device 704 or any suitable computer-readable medium and may beexecuted by the processor 702 or any other suitable processor. In someimplementations, the program code described above, the deep virtualstereo odometry calculation module 125, and the stacked architecturemodule 200, are stored in the memory device 704, as depicted in FIG. 7.In additional or alternative implementations, one or more of the deepvirtual stereo odometry calculation module 125, the stacked architecturemodule 200, and the program code described above are stored in one ormore memory devices accessible via a data network, such as a memorydevice accessible via a cloud service.

The computing system 701 depicted in FIG. 7 also includes at least onenetwork interface 710. The network interface 710 includes any device orgroup of devices suitable for establishing a wired or wireless dataconnection to one or more data networks 712. Non-limiting examples ofthe network interface 710 include an Ethernet network adapter, a modem,and/or the like. In some cases, the computing system 701 is able tocommunicate with the camera sensor 105 using the network interface 710.Although FIG. 7 depicts the camera sensor 105 as connected to computingsystem 701 via the networks 712, other implementations are possible,including the camera sensor 105 operating as a component of computingsystem 701, such as input components connected via I/O interface 708.

GENERAL CONSIDERATIONS

Numerous specific details are set forth herein to provide a thoroughunderstanding of the claimed subject matter. However, those skilled inthe art will understand that the claimed subject matter may be practicedwithout these specific details. In other instances, methods,apparatuses, or systems that would be known by one of ordinary skillhave not been described in detail so as not to obscure claimed subjectmatter.

Unless specifically stated otherwise, it is appreciated that throughoutthis specification discussions utilizing terms such as “processing,”“computing,” “calculating,” “determining,” and “identifying” or the likerefer to actions or processes of a computing device, such as one or morecomputers or a similar electronic computing device or devices, thatmanipulate or transform data represented as physical electronic ormagnetic quantities within memories, registers, or other informationstorage devices, transmission devices, or display devices of thecomputing platform.

The system or systems discussed herein are not limited to any particularhardware architecture or configuration. A computing device can includeany suitable arrangement of components that provides a resultconditioned on one or more inputs. Suitable computing devices includemultipurpose microprocessor-based computer systems accessing storedsoftware that programs or configures the computing system from a generalpurpose computing apparatus to a specialized computing apparatusimplementing one or more implementations of the present subject matter.Any suitable programming, scripting, or other type of language orcombinations of languages may be used to implement the teachingscontained herein in software to be used in programming or configuring acomputing device.

Implementations of the methods disclosed herein may be performed in theoperation of such computing devices. The order of the blocks presentedin the examples above can be varied—for example, blocks can bere-ordered, combined, and/or broken into sub-blocks. Certain blocks orprocesses can be performed in parallel.

The use of “adapted to” or “configured to” herein is meant as open andinclusive language that does not foreclose devices adapted to orconfigured to perform additional tasks or steps. Additionally, the useof “based on” is meant to be open and inclusive, in that a process,step, calculation, or other action “based on” one or more recitedconditions or values may, in practice, be based on additional conditionsor values beyond those recited. Headings, lists, and numbering includedherein are for ease of explanation only and are not meant to belimiting.

While the present subject matter has been described in detail withrespect to specific implementations thereof, it will be appreciated thatthose skilled in the art, upon attaining an understanding of theforegoing, may readily produce alterations to, variations of, andequivalents to such implementations. Accordingly, it should beunderstood that the present disclosure has been presented for purposesof example rather than limitation, and does not preclude inclusion ofsuch modifications, variations, and/or additions to the present subjectmatter as would be readily apparent to one of ordinary skill in the art.

What is claimed is:
 1. A monocular visual odometry system, comprising: astacked architecture module configured to perform operations comprising:receiving camera frame data from a monocular camera sensor; andgenerating a depth map of the camera frame data; and a deep virtualstereo odometry calculation module configured to perform operationscomprising: receiving the camera frame data from the monocular camerasensor and the depth map from the stacked architecture module;initializing a keyframe of the camera frame data using the depth map ofthe camera frame data; determining a photometric error based on a set ofobservation points extracted from the keyframe and a set of referencepoints extracted from a set of reference camera frames of the cameraframe data; determining a virtual stereo photometric term using thedepth map of the camera frame data; optimizing a total photometricenergy function comprising the photometric error and the virtual stereophotometric term; generating a positional parameter of the monocularvisual odometry system using the total photometric energy function; andproviding the positional parameter to an autonomous system.
 2. Themonocular visual odometry system of claim 1, wherein the stackedarchitecture module comprises a first encoder-decoder architecturemodule and a residual encoder-decoder architecture module.
 3. Themonocular visual odometry system of claim 1, wherein the stackedarchitecture module is configured to perform operations furthercomprising: generating, by an encoder-decoder neural network, a firstdisparity map of the camera frame data; generating, by a residualencoder-decoder neural network, a residual disparity map of the cameraframe data; and generating the depth map by combining the firstdisparity map and the residual disparity map using element-wisesummation.
 4. The monocular visual odometry system of claim 1, whereinthe stacked architecture module is trainable by minimizing a total lossterm comprising a self-supervised loss term, a supervised loss term, aleft-right consistency loss term, a smoothness term, an occlusionregularization term, or any combination thereof.
 5. The monocular visualodometry system of claim 1, further comprising: the autonomous system,wherein the autonomous system is controlled using the positionalparameter.
 6. The monocular visual odometry system of claim 1, whereinthe photometric error is based on a comparison of the set of observationpoints and the set of reference points.
 7. A method, comprising:receiving camera frame data from a monocular camera sensor; generating adepth map of the camera frame data; initializing a keyframe of thecamera frame data using the depth map of the camera frame data;determining a photometric error based on a set of observation pointsextracted from the keyframe and a set of reference points extracted froma set of reference camera frames of the camera frame data; determining avirtual stereo photometric term using the depth map of the camera framedata; optimizing a total photometric energy function comprising thephotometric error and the virtual stereo photometric term; generating apositional parameter of the monocular camera sensor using the totalphotometric energy function; and providing the positional parameter toan autonomous system.
 8. The method of claim 7, further comprising:controlling operation of the autonomous system using the positionalparameter.
 9. The method of claim 7, wherein the depth map comprises aleft disparity map and a right disparity map.
 10. The method of claim 7,wherein the virtual stereo photometric term is generated for each pointof the set of observation points.
 11. The method of claim 7, wherein thephotometric error is based on a comparison of the set of observationpoints and the set of reference points.
 12. The method of claim 7,further comprising: generating a first disparity map of the camera framedata; generating a residual disparity map of the camera frame data; andgenerating the depth map by combining the first disparity map and theresidual disparity map using element-wise summation.
 13. Anon-transitory computer-readable medium embodying program code foroperating a monocular visual odometry system, the program codecomprising instructions which, when executed by a processor, cause theprocessor to perform operations comprising: receiving camera frame datafrom a monocular camera sensor; generating a depth map of the cameraframe data; initializing a keyframe of the camera frame data using thedepth map of the camera frame data; determining a photometric errorbased on a set of observation points extracted from the keyframe and aset of reference points extracted from a set of reference camera framesof the camera frame data; determining a virtual stereo photometric termusing the depth map of the camera frame data; optimizing a totalphotometric energy function comprising the photometric error and thevirtual stereo photometric term; generating a positional parameter ofthe monocular camera sensor using the total photometric energy function;and providing the positional parameter to an autonomous system.
 14. Thenon-transitory computer-readable medium of claim 13, wherein the depthmap is generated using a stacked architecture module comprising a firstencoder-decoder architecture module stacked with a residualencoder-decoder architecture module.
 15. The non-transitorycomputer-readable medium of claim 14, wherein the instructions cause theprocessor to perform further operations comprising: training the stackedarchitecture module by minimizing a total loss term comprising aself-supervised loss term, a supervised loss term, a left-rightconsistency loss term, a smoothness term, an occlusion regularizationterm, or any combination thereof.
 16. The non-transitorycomputer-readable medium of claim 13, wherein the instructions cause theprocessor to perform further operations comprising: generating a firstdisparity map of the camera frame data; generating a residual disparitymap of the camera frame data; and generating the depth map by combiningthe first disparity map and the residual disparity map usingelement-wise summation.
 17. The non-transitory computer-readable mediumof claim 13, wherein the photometric error is based on a comparison ofthe set of observation points and the set of reference points.
 18. Thenon-transitory computer-readable medium of claim 13, wherein theinstructions cause the processor to perform further operationscomprising: controlling operation of the autonomous system using thepositional parameter.
 19. The non-transitory computer-readable medium ofclaim 13, wherein the depth map comprises a left disparity map and aright disparity map.
 20. The non-transitory computer-readable medium ofclaim 13, wherein the virtual stereo photometric term comprises avirtual projected coordinate of each observation point of the set ofobservation points using a vector comprising a virtual stereo baseline.